1. Field of the Invention
This invention relates to films and sheets formed from blends of polyethylene terephthalate and polycarbonate resins useful as cook-in-trays.
2. Discussion of the Prior Art
Our U.S. Pat. application with William Sacks, Ser. No. 489,017 filed July 16, 1974, U.S. Pat. No. 3,956,229 describes films and sheets formed from blends of polyethylene terephthalate and polycarbonate resins and their production. Such films and sheets are useful to form cook-in-trays which are substitutes for aluminum and other conventional trays. As described in said application, a film or sheet is formed from a blend of about 60 to 85 parts by weight of polyethylene terephthalate having an intrinsic viscosity of at least about 0.90 and correspondingly about 40 to 15 parts by weight of a polycarbonate, with the polyethylene terephthalate fraction having a degree of crystallinity in the range of about 20 to 40%.
It has now been found that while such compositions are suitable for use as cooking containers, in some cases the trays exhibit an initial distortion while in the oven, which detracts from their aesthetic appearance. This distortion is believed to be caused by a slight initial softening and subsequent shrinkage of the trays as further crystallization of the polyethylene terephthalate occurs. It would be desirable if films and sheets could be formed from such compositions which, when formed into cook-in-trays and placed in an oven, do not exhibit a distortion in shape.